ACI Structural Journal/March-April 2010 157

ACI Structural Journal, V. 107, No. 2, March-April 2010.MS No. S-2008-256.R1 received April 17, 2009, and reviewed under Institute publication

policies. Copyright © 2010, American Concrete Institute. All rights reserved, includingthe making of copies unless permission is obtained from the copyright proprietors. Pertinentdiscussion including author’s closure, if any, will be published in the January-February 2011ACI Structural Journal if the discussion is received by September 1, 2010.

ACI STRUCTURAL JOURNAL TECHNICAL PAPER

Minimum thickness provisions for one- and two-way slabs providea well-established approach for deflection control. Variousnational design codes and specifications have approached theseprovisions from different perspectives. Concerns have been raisedabout the range of the validity of current ACI Code provisions.This paper compares the ACI Code provisions with several nationalcodes and an equation proposed by the authors to incorporate the maindesign variables affecting deflection control. Based on the resultsof the comparison, a recommendation is made to adopt theproposed equation, retaining the current values as upper limits.

Keywords: deflection; minimum thickness; reinforced concrete; serviceability.

INTRODUCTIONThe ACI Code (ACI Committee 318 2008) provides

minimum thickness values for one- and two-way slabs,under prescribed conditions, as a function of span length,boundary conditions, and steel yield strength as a basis fordeflection control. These provisions have remained essentiallyunchanged since 1971 and are attractive due to theirsimplicity. A number of authors have raised questions aboutthe validity of the current provisions under certain designconditions (Grossman 1981; Rangan 1982; Gilbert 1985;Hwang and Chang 1996; Scanlon and Choi 1999; Scanlon etal. 2001; Bondy 2005). To address these questions, theauthors proposed a unified equation that could be applied toone- and two-way slabs as well as beams (Scanlon and Lee2006). Building codes and standards in other parts of theworld also provide minimum thickness or span-depth criteriafor deflection control. The objective of this paper is tocompare the current ACI provisions with the authors’proposed equation and provisions currently used in othercodes and standards. The provisions selected for comparisonare those incorporated in the British Standard for Design ofConcrete Structures (British Standards Institution 1997),Eurocode 2: Design of Concrete Structures (British StandardsInstitution 2004), and the Australian Standard for ConcreteStructures (AS Committee BD-002 2001). Similarities anddifferences among the various provisions are identifiedand recommendations for changes to the ACI Code arepresented. The scope of this paper is restricted to one- andtwo-way slab systems covered by provisions of the ACICode. Flat plates with small shear caps that do not qualify asdrop panels according to ACI 318-08 could be considered asflat plates with an appropriate definition of clear span usingSection 13.1.2 of ACI 318-08. A separate study is beingconducted to compare code provisions for deflection controlof beams.

RESEARCH SIGNIFICANCEMinimum thickness provisions in ACI 318-08 have

remained unchanged since 1971. This paper presents a

review of the current provisions, including comparisons withseveral national codes, and provides recommendations forchanges to ACI 318-08 provisions for one- and two-waynonprestressed construction.

MINIMUM THICKNESS PROVISIONSMinimum thickness provisions are attractive as a means of

deflection control due to their simplicity. In this paper, fourdifferent codes, including ACI 318-08, BS 8110-1:1997,Eurocode 2, and Australian Standard AS 3600-2001 and theproposed approach of Scanlon and Lee (2006) are comparedfor one- and two-way slabs. The selected codes have beenused for many construction projects, not only for theirhomelands but also in other countries including those inAfrica, Asia, and South America. ACI 318 provisions arebased on member depth, whereas other codes are based onreinforcement effective depth. To allow for comparison ofthe various methods considered, 1 in. (25.4 mm) was addedto the effective depth for cases where minimum thicknesswas based on effective depth. Comparisons were thus basedon total member depth. A brief description of the variouscode provisions is provided as follows with reference to thesummary provided in Table 1.

ACI Building Code (ACI 318-08)ACI 318-08 provides minimum thickness provisions as a

fraction of span length for both one- and two-way slabs, asshown in Table 1. The minimum thickness values areindependent of applied load including live and dead loads,and no limits are specified on the applicable range of spanlengths. Modification factors are provided for steel yieldstrength and lightweight concrete.

British Standard Code (BS EN 8110-1:1997)For the minimum thickness requirements, BS EN 8110-1:1997

provides basic span-to-effective depth ratios that varyaccording to support conditions, including simply supported,continuous, and cantilever. In addition to the basic span-to-effective depth ratio, a modification factor is provided fortension reinforcement determined by tensile strength ofreinforcements and design ultimate moment at the center ofthe member (for cantilever, at the support). A modificationfactor for compression reinforcement is also used. Additionally,BS EN 8110-1:1997 specifies modification factors for spans

Title no. 107-S15

Comparison of One- and Two-Way Slab Minimum Thickness Provisions in Building Codes and Standardsby Young Hak Lee and Andrew Scanlon

ACI Structural Journal/March-April 2010158

greater than 32.8 ft (10 m) and for flat plates, as indicated inTable 1.

Eurocode 2 (BS EN 1992-1-1:2004)Minimum thickness in the Eurocode 2 provisions is based

on a reinforcement ratio depending on whether theactual reinforcement ratio is larger than or smaller than agiven reference reinforcement ratio. Because the rein-forcement ratio cannot be determined until the memberdepth is established, an initial estimate must be made of thereinforcement ratio. If the span length exceeds 23.0 ft (7 m),the depth is multiplied by 23.0/span length (7/span length) toaccount for an increased self-weight of the member as span

length increases. For flat plates, the depth is multiplied by27.9/span length (8.5/span length).

The minimum thickness requirement of Eurocode 2 can beapplied to both beams and slabs and depends on the rein-forcement ratio calculated from moment at the center of themember and compressive strength of the concrete. Thedifference between one- and two-way construction,however, is not well-defined in the application of theminimum thickness equations.

Australian Standard (AS 3600-2001)The current Australian Standard, AS 3600-2001, provides

a span-to-effective depth equation as listed in Table 1, takinginto account the effects of cracking, long-term effects, andload conditions. The equation is similar in form to theequation proposed by Scanlon and Choi (1999) which, inturn, is based on a simplification of the form originallyproposed by Rangan (1982).

Unified equation proposed by Scanlonand Lee (2006)

Scanlon and Lee (2006) proposed a generalized minimumthickness equation for one- and two-way nonprestressedconstruction in terms of span-depth ratios considering

ACI member Young Hak Lee is an Assistant Professor in the Department of ArchitecturalEngineering at Kyung Hee University, Yongin, Korea. He is a member of ACI Committee 435,Deflection of Concrete Building Structures. His research interests include the serviceabilityof reinforced and prestressed concrete members, and developing analytical models ofconcrete structures.

Andrew Scanlon, FACI, is a Professor in the Department of Civil and EnvironmentalEngineering at the Pennsylvania State University, University Park, PA. He is Chair ofACI Committee 435, Deflection of Concrete Building Structures, and a member of ACICommittees 224, Cracking; 342, Evaluation of Concrete Bridges and Bridge Elements;and 348, Structural Safety.

Table 1—Minimum thickness provisions for slabs

ACI 318-08

Minimum thickness of nonprestressed one-way slabs unless deflections are calculated

Simply supported One end continuous

Both endscontinuous Cantilever

l/20 l/24 l/28 l/10

Minimum thickness of two-way slabs without interior beams

fy,psi

Without drop panels

Exterior panels Interior panels

Without edge

beamsWith edge beams —

60,000 ln /30 ln /33 ln /33

l is span length of one-way slabln is length of clear span measured face-to-face of supports

For slabs with beams spanning between supports on all sides

αfm ≤ 0.2Slabs without drop panels - 5 in.Slabs with drop panels - 4 in.0.2 ≤ αfm ≤ 2

αfm > 2

αfm is average value of αf for all beams on edges of panelαf is ratio of flexural stiffness of beam section to flexural stiffness of width of slab

AS 3600-2001

Lef is effective span, taken as less of (ln + d) and l;d is effective depth of cross section;Δ / Lef is deflection limit;Fd.ef is effective design load, per unit area;k3 = 1.0 for one-way slab, rectangular slabs supported on four sides

= 0.95 for two-way flat slab without drop panels;k4 is deflection constant which may be taken as:

(a) for simply supported slabs, 1.6; or (b) for continuous slabs, where in adjoining spans ratio of longer span to shorter span does not exceed 1.2 where no end span is longer than an interior span-(i) 2.0 in an end span; or (ii) 2.4 in interior spans; and(c) for edge-supported slabs k4 varies from 1.7 to 2.0 (Table 9.3.4.2 in AS 3600-2001).

hln 0.8

fy

200 000,---------------------+⎝ ⎠

⎛ ⎞

36 5β αfm 0.2–( )+---------------------------------------------- Not less than 5 in. =

hln 0.8

fy

200 000,---------------------+⎝ ⎠

⎛ ⎞

36 9β+--------------------------------------------- Not less than 3.5 in. =

Lef d⁄ k3k4Δ Lef⁄( )Ec

Fd .ef

-------------------------1 3⁄

=

ACI Structural Journal/March-April 2010 159

applied loads, long-term multipliers, effects of cracking,and target deflection-to-span limitations. The equation isbased on using an effective moment of inertia, Ie, equal toone-half of the gross moment of inertia, Ig. This approximationallows the thickness to be selected without knowing thereinforcement ratio, although an initial estimate of thedepth is required to compute dead load due to self-weight.The unified equation was developed from the equationsuggested by Scanlon and Choi (1999) for one-way slabsbased on a simplified form of the approach proposed byRangan (1982) for one-way construction and extended totwo-way construction by Gilbert (1985).

PARAMETRIC STUDYA parametric study was performed to evaluate the effects

of design variables on the minimum thickness and tocompare values calculated from the various design codes andthe Scanlon and Lee (2006) unified equation. The parametersconsidered herein include the following.

Span length—The following span lengths were used torepresent ranges typically encountered in practice:• 10, 15, 20, 25, 30, 35, and 40 ft (3.05, 4.57, 6.10, 7.62,

9.14, 10.67, and 12.19 m) for one-way slabs;• 10, 15, 20, 25, and 30 ft (3.05, 4.57, 6.10, 7.62, and

9.14 m) for flat plates (square);

• 10, 15, and 20 ft (3.05, 4.57, and 6.10 m) for edgesupported two-way slabs; and

• Live load—Live loads are based on ASCE/SEI 7 (2005)provisions for: a) office occupancy plus allowance forpartitions: 70 psf (3.4 kPa); (b) for example, assemblyand restaurant: 100 psf (4.87 kPa); and (c) storage (lightto heavy): 200 psf (9.74 kPa).

The following design parameters were held constant:• Concrete compressive strength: 4000 psi (27.58 MPa);• Yield strength of reinforcement: 60,000 psi (413.69 MPa);• Superimposed dead load: 15 psf (0.73 kPa);• Sustained live load: (a) 20 psf (0.97 kPa) for live load equal

to 70 psf (3.4 kPa) and 100 psf (4.87 kPa); and (b) 50 psf(2.44 kPa) for live load equal to 200 psf (9.74 kPa); and

• Long-time multiplier λ: 2.Target allowable deflections for AS 3600-2001 and the

unified equation were taken as l/240 and l/480. All of theprovisions considered except ACI 318 consider variation oflive load in establishing minimum thickness. Design parametersconsidered in the various codes are summarized in Table 2.Results of the parametric study are presented in thefollowing for one-way slabs, flat plates, and edge-supportedslabs. Deflection limits are those corresponding to deflectionsoccurring after installation of nonstructural elements.

Table 1—Minimum thickness provisions for slabs (cont.)

BS 8110-1

Basic span/effective depth ratios for rectangular section

Modification factor for tension reinforcement

M is design ultimate moment at center of span or, for cantilever, at support;fs is estimated design service stress in tension reinforcement;fy is yield strength of reinforcement;b is effective width of rectangular beam;d is effective depth;

For spans exceeding 10 m, Table 3.9 should be multiplied by 10/span, except for cantilevers where the design should be justified by calculation.For flat plate, span/effective depth ratio should be multiplied by 0.9.

Support conditions Rectangular section

CantileverSimply supported

Continuous

72026

Eurocode 2

If ρ ≤ ρο

If ρ > ρο

K is factor to take into account different structural systems: (a) simply supported 1.0; (b) one end continuous 1.3; and (c) both end continuous 1.5;

ρo is reference reinforcement ratio, = ;ρ is required tension reinforcement ratio at midspan to resist

moment due to design loads (at support for cantilevers);ρ′ is required compression reinforcement ratio at midspan to

resist moment due to design loads (at support for cantilevers);fck is specified compressive strength of concrete, in MPa units; andl is span length.

Scanlon and Lee’s proposal

(U.S. Customary Units)

(SI Units)

Ws is sustained load (psf [slabs]; plf [beams]); (Pa [slabs];N/m [beams]);

WL(add) is additional live load (psf [slabs]; plf [beams]); (Pa[slabs]; N/m [beams]);

β = 1, except β is long span/short span ≤ 2.0 for edge-supported slabs;

κ is deflection coefficient depending on support condition: equals 5 for simply supported, 1.4 for both ends continuous, 2 for one end continuous, and 48 for fixed end cantilever;

kDP = 1, except kDP = 1.35 for slab with drop panels;kSS = 1, except kSS = 1.35 for column supported two-way

slab systems;kAR = 1, except kAR = 0.2 + 0.4β for edge-supported slabs;b = 12 in. (1000 mm for SI) for one- and two-way slabs = beam

width (= web width, bw for T-beams) (in. for U.S. Customary Units and mm for SI Units);

(Δinc)allow is required incremental deflection limit; and λ is long-time multiplier for sustained loads (ACI 318,

Section 9.5.2.5).

0.55477 fs–( )

120 0.9 M

bd2--------+⎝ ⎠

⎛ ⎞------------------------------------- 2.0 fs

23--- fy=≤+=

l

d--- K 11 1.5 fck

ρo

ρ----- 32+ fck

ρo

ρ----- 1–⎝ ⎠

⎛ ⎞3 2⁄

+=

l

d--- K 11 1.5 fck

ρo

ρ ρ′–-------------- 1

12------+ fck

ρ′ρo

-----+=

fck10

3–

ln

h---- β

Δinc

l---------⎝ ⎠

⎛ ⎞allow

2400kDPEc b 12⁄( )κkARkss λWs WL add( )+( )--------------------------------------------------------------

1 3⁄

=

ln

h---- β

Δinc

l---------⎝ ⎠

⎛ ⎞allow

0.0167kDPEcbκkARkss λWs WL add( )+( )--------------------------------------------------------------

1 3⁄

=

160 ACI Structural Journal/March-April 2010

One-way slabsFigures 1(a) to (c) show span-depth ratios versus span

length for one-way slabs with various end conditions for aconstant live load of 70 psf (3.4 kPa) and a deflection limitof l/240. For this case, ACI 318 values are consistently lowerthan all others for spans up to approximately 40 ft (12.19 m).All provisions, except ACI 318, show a general trend ofdecreasing span-depth ratio with increasing span length.Figures 2(a) to (c) show the corresponding results for adeflection limit of l/480. It should be noted that the minimum

thickness values given in ACI 318 are intended for use with slabsnot supporting or attached to nonstructural elements likely to bedamaged by large deflections, that is, the l/240 limit. Theseresults suggest, however, that ACI 318 values should besatisfactory in most cases to satisfy the l/480 limit for liveload up to 70 psf (3.4 kPa), except for the simply supported casewhere the ACI 318 values are conservative compared with otherprovisions up to a span of approximately 20 ft (6.10 m).

Effects of varying live load according to the provisionsconsidered are shown in Fig. 3 for a deflection limit of l/480.

Fig. 1—Span-depth ratio as function of span length—one-wayslabs, l/240: (a) simply supported: live load = 70 psf (3.4 kPa);(b) one end continuous: live load = 70 psf (3.4 kPa); and (c)both ends continuous: live load = 70 psf (3.4 kPa).

Fig. 2—Span-depth ratio as function of span length—one-wayslabs, l/480: (a) simply supported: live load = 70 psf (3.4 kPa);(b) one end continuous: live load = 70 psf (3.4 kPa); and (c)both ends continuous: live load = 70 psf (3.4 kPa).

Table 2—Design parameters considered in minimum thickness provisions

Design parameters

Design parameters considered

ACI 318-08 BS 8110-1 Eurocode 2 AS 3600-2001 Scanlon and Lee’s proposal

Boundary condition Yes Yes Yes Yes Yes

Span length Yes Yes Yes Yes Yes

Live load No Yes Yes Yes Yes

Superimposed dead load No No No No Yes

Allowable deflection limit No No No Yes Yes

ACI Structural Journal/March-April 2010 161

Values obtained using ACI 318, Table 9.5(a), are used as areference, although strictly speaking, the ACI 318 values arenot applicable to the deflection limit of l/480. The simplysupported case is selected as the basis for comparison. In allcases except ACI 318, the calculated span-depth ratiodecreases as live load increases. The BS 8110-1:1997 span-depth ratios are less conservative than ACI 318 up to a span ofapproximately 40 ft (12.19 m). Eurocode 2 provides span-depth ratios that are higher than the ACI 318 values forspans greater than 35 ft (10.67 m) and live load less than100 psf (4.87 kPa). For the 200 psf (9.74 kPa) live load case,Eurocode 2 provides lower span-depth ratio than ACI 318for spans greater than approximately 22 ft (6.71 m). AS3600-2001 and Scanlon and Lee (2006) show similar trendsproviding span-depth ratios that are more conservative thanthe ACI 318 values over a wider range of span lengths thanBS 8110-1:1997 and Eurocode 2.

Flat platesFigure 4 shows the span-depth ratio plotted against span

length for an interior panel of a flat plate for l/240 and l/480deflection limits, and a live load of 70 psf (3.4 kPa). Figure 4(a)shows that the ACI Code values are conservative compared tothe other provisions for the l/240 deflection limit. For the l/480case, however, the AS 3600-2001 and Scanlon and Lee (2006)values are more conservative for spans greater than approx-imately 15 ft (4.57 m). Figure 5 shows the effect of increasinglive load for the l/480 limit. In all cases for heavy live loads(200 psf [9.74 kPa]), the ACI values are unconservativecompared with the other provisions.

Edge-supported two-way slabsFigures 6 and 7 show the comparison between ACI 318

and the other provisions for two-way edge-supported slabs ofvarying aspect ratios and live loads. In general, the ACI 318values are seen to be conservative compared to the otherprovisions while there is a wide variation in the valuesobtained with the various provisions.

DISCUSSION OF RESULTSResults of the parametric study indicate that ACI

minimum thickness values for one-way slabs and edge-supported two-way slabs are generally conservativecompared with the other provisions considered for spanlengths up to approximately 40 ft (12.19 m) for both the l/240and l/480 deflection limits. It should be noted that, strictlyspeaking, the ACI 318-08 minimum thickness values forone-way slabs should only be used for slabs “not supporting

Fig. 3—Span-depth ratio as function of span length and variable live loads—one-wayslabs: (a) BS 8110-1: simply supported, l/480; (b) Eurocode 2: simply supported, l/480;(c) AS 3600-2001: simply supported, l/480; and (d) unified equation proposed by Scanlonand Lee (2006): simply supported, l/480.

Fig. 4—Span-depth ratio as function of span length—flatplates: (a) live load = 70 psf (3.4 kPa), l/240; and (b) liveload = 70 psf (3.4 kPa), l/480.

162 ACI Structural Journal/March-April 2010

or attached to non-structural elements likely to be damagedby large deflections.” This is consistent with the generallyacceptable performance over the years of one-way slabs andedge-supported two-way slabs. For heavy live loads and heavysuperimposed dead loads (greater than 100 psf [4.87 kPa]), amore detailed deflection evaluation is recommended.

The situation with respect to flat plates is somewhatdifferent. For the l/240 limit, the ACI minimum thicknessvalues appear to be adequate for the span range consideredand a specified live load of 70 psf (3.4 kPa). For the l/480case, however, the AS 3600-2001 and Scanlon and Lee(2006) provisions suggest that the current ACI 318 valuesare generally unconservative for the span and live load rangeconsidered. This is particularly the case for longer spans andhigher load levels. These results suggest that the currentACI 318-08 minimum thickness values need to be reevaluatedin terms of their applicability to slabs “supporting non-structuralelements likely to be damaged by large deflections.”

CONCLUSIONS AND RECOMMENDATIONSVarious design provisions including ACI 318-08, BS

8110-1:1997, Eurocode 2, and AS 3600-2001 and the unifiedequation proposed by Scanlon and Lee (2006) are comparedin terms of minimum thickness for one- and two-way slabs.The effects of design parameters such as support condition,span length, and applied load are evaluated. The results indicatethat ACI 318 provisions need to be revised to cover the rangeof design parameters that are prevalent in current practice.The results of the parametric study suggest that while theseminimum thickness values are easy to apply, limitations need tobe placed on the applicability of current ACI values. Inparticular, the ACI values for flat plates (and flat slabs) seemto be adequate for the l/240 limit for typical spans andloading but may be inadequate in many cases to satisfy thel/480 limit. It is recommended that the Scanlon/Lee equationfor minimum thickness of one-way slabs, flat plates, and flatslabs be adopted by ACI 318 but not less than values given by thecurrent limits. The advantage of the proposed equation is that it isrelatively easy to apply and covers a wider range of designconditions than seems to have been anticipated when thecurrent provision were introduced. Given the approximationsinvolved in the proposed equation and many years of experiencewith the current provisions, however, it is considered prudent toretain the current minimum thickness values when the proposedequation produces a lower thickness value than the current

Fig. 6—Span-depth ratio as function of span length: edge-supported slabs (short span = 15 ft [4.57 m] and αfm = 2 forACI 318-08 requirement): (a) live load = 70 psf (3.4 kPa),l/240; and (b) live load = 70 psf (3.4 kPa), l/480.

Fig. 5—Span-depth ratio as function of span length and variable live loads—flat plates:(a) BS 8110-1, l/480; (b) Eurocode 2, l/480; (c) AS 3600-2001, l/480; and (d) unifiedequation proposed by Scanlon and Lee (2006), l/480.

ACI Structural Journal/March-April 2010 163

provisions. The proposed minimum thickness equationshould not be applied when slabs are over-loaded before thespecified 28-day concrete strength has been reached unlessappropriate adjustments to the equation have been made toaccount for such early age loading.

ACKNOWLEDGMENTSThis work was supported by a grant from the Kyung Hee University in

2009 (KHU-20090758).

REFERENCESACI Committee 318, 2008, “Building Code Requirements for Structural

Concrete (ACI 318-08) and Commentary,” American Concrete Institute,Farmington Hills, MI, 473 pp.

AS 3600-2001, 2001, “Australian Standard for Concrete Structures,”Standards Australia, Sydney, Australia, 175 pp.

ASCE/SEI 7, 2005, Minimum Design Loads for Buildings and OtherStructures, American Society of Civil Engineers, 388 pp.

Bondy, K. B., 2005, “ACI Code Deflection Requirements—Time for aChange?” Serviceability of Concrete: A Symposium Honoring Dr. Edward G.Nawy, SP-255, F. Barth, ed., American Concrete Institute, FarmingtonHills, MI, pp. 133-146.

BS EN 8110-1:1997, 1997, “British Standard Code: Design of ConcreteStructures,” British Standards Institution, London, UK, 159 pp.

BS EN 1992-1-1:2004, 2004, “Eurocode 2: Design of Concrete Structures.General Rules and Rules for Buildings,” British Standards Institution,London, UK, 230 pp.

Gilbert, R. I., 1985, “Deflection Control of Slabs Using Allowable Span-to-Depth Ratios,” ACI Structural Journal, V. 82, No. 1, Jan.-Feb., pp. 67-72.

Grossman, J. S., 1981, “Simplified Computations for Effective Momentof Inertia, Ie and Minimum Thickness to Avoid Deflection Calculations,”ACI Structural Journal, V. 78, No. 6, Nov.-Dec., pp. 423-439.

Hwang, S.-J., and Chang, K.-Y., 1996, “Deflection Control of Two-WayReinforced Concrete Slabs,” Journal of Structural Engineering, ASCE, V. 122,No. 2, pp. 160-168.

Rangan, B. V., 1982, “Control of Beam Deflections by Allowable Span-to-Depth Ratios,” ACI Structural Journal, V. 79, No. 5, Sept.-Oct., pp. 372-377.

Scanlon, A.; Cagley Orsak, D. R.; and Buettner, D. R., 2001, “ACI 318Code Requirements for Deflection Control: A Critical Review,” CodeProvisions for Deflection Control in Concrete Structures, SP-203, E. G.Nawy and A. Scanlon, eds., American Concrete Institute, FarmingtonHills, MI, pp. 1-13.

Scanlon, A., and Choi, B.-S., 1999, “Evaluation of ACI 318 MinimumThickness Requirements for One-Way Slabs,” ACI Structural Journal,V. 96, No. 4, July-Aug., pp. 616-621.

Scanlon, A., and Lee, Y. H., 2006, “Unified Span-to-Depth Ratio Equationfor Nonprestressed Concrete Beams and Slabs,” ACI Structural Journal,V. 103, No. 1, Jan.-Feb., pp. 142-148.

Fig. 7—Span-depth ratio as function of span length and variable live loads: edge-supportedslabs (short span = 15 ft [4.57 m] and αfm = 2 for ACI 318-08 requirement): (a) BS 8110-1,l/480; (b) Eurocode 2 (BS EN 2004), l/480; (c) AS 3600-2001, l/480; and (d) unifiedequation proposed by Scanlon and Lee (2006), l/480.